The field is internal combustion engines, particularly two-stroke cycle, opposed-piston engines. More specifically, the field is related to on-board diagnostic monitoring of the air handling systems of opposed-piston engines equipped with superchargers to determine whether the superchargers are functioning properly. The field also includes diagnostic monitoring of opposed-piston air handling elements associated with supercharger operations.
A two-stroke cycle engine is an internal combustion engine that completes a cycle of operation with a single complete rotation of a crankshaft and two strokes of a piston connected to the crankshaft. The strokes are typically denoted as compression and power strokes. One example of a two-stroke cycle engine is an opposed-piston engine in which two pistons are disposed in the bore of a cylinder for reciprocating movement in opposing directions along the central axis of the cylinder. Each piston moves between a bottom center (BC) location where it is nearest one end of the cylinder and a top center (TC) location where it is furthest from the one end. The cylinder has ports formed in the cylinder sidewall near respective BC piston locations. Each of the opposed pistons controls one of the ports, opening the port as it moves to its BC location, and closing the port as it moves from BC toward its TC location. One of the ports serves to admit charge air (sometimes called “scavenging air”) into the bore, the other provides passage for the products of combustion out of the bore; these are respectively termed “intake” and “exhaust” ports (in some descriptions, intake ports are referred to as “air” ports or “scavenge” ports). In a uniflow-scavenged opposed-piston engine, pressurized charge air enters a cylinder through its intake port as exhaust gas flows out of its exhaust port, thus gas flows through the cylinder in a single direction (“uniflow”)—from intake port to exhaust port.
With reference to FIG. 1, a two-stroke cycle internal combustion engine is embodied in an opposed-piston engine 10 having at least one ported cylinder 50. For example, the engine may have one ported cylinder, two ported cylinders, three ported cylinders, or four or more ported cylinders. Each ported cylinder 50 has a bore 52 and longitudinally spaced intake and exhaust ports 54 and 56 formed or machined in respective ends of a cylinder wall. Each of the intake and exhaust ports 54 and 56 includes one or more circumferential arrays of openings in which adjacent openings are separated by a solid bridge. In some descriptions, each opening is referred to as a “port”; however, the construction of a circumferential array of such “ports” is no different than the port constructions shown in FIG. 1. Pistons 60 and 62 are slideably disposed in the bore 52 of each cylinder with their end surfaces 61 and 63 opposing one another. Movements of the pistons 60 control the operations of the intake ports 54. Movements of the pistons 62 control the operations of the exhaust ports 56. Thus, the ports 54 and 56 are referred to as “piston controlled ports”. Pistons 60 controlling the exhaust ports (“exhaust pistons”) are coupled to a crankshaft 71. Pistons 62 controlling the intake ports of the engine (“intake ports”) are coupled to a crankshaft 72.
As pistons 60 and 62 approach respective TC locations, a combustion chamber is defined in the bore 52 between the end surfaces 61 and 63. Fuel is injected directly into the combustion chamber through at least one fuel injector nozzle 70 positioned in an opening through the sidewall of a cylinder 50. The fuel mixes with charge air admitted through the intake port 54. As the mixture is compressed between the end surfaces it reaches a temperature that causes the fuel to ignite; in some instances, ignition may be assisted, as by spark or glow plugs. Combustion follows.
The engine 10 includes an air handling system 80 that manages the transport of charge air provided to, and exhaust gas produced by, the engine 10. A representative air handling system construction includes a charge air subsystem and an exhaust subsystem. The charge air subsystem receives and compresses air and includes a charge air channel that delivers the compressed air to the intake port or ports of the engine. One or more stages of compression may be provided. For example, the charge air subsystem may comprise one or both of a turbine-driven compressor and a supercharger. The charge air channel typically includes at least one air cooler that is coupled to receive and cool the charge air (or a mixture of gasses including charge air) before delivery to the intake port or ports of the engine. The exhaust subsystem includes an exhaust channel that transports exhaust products from exhaust ports of the engine for delivery to other exhaust components.
A typical air handling system for an opposed-piston engine is shown in FIG. 1. The air handling system 80 may comprise a turbocharger 120 with a turbine 121 and a compressor 122 that rotate on a common shaft 123. The turbine 121 is coupled to the exhaust subsystem and the compressor 122 is coupled to the charge air subsystem. The turbocharger 120 extracts energy from exhaust gas that exits the exhaust ports 56 and flows into an exhaust channel 124 directly from the exhaust port or ports 56, or from an exhaust manifold 125 or an exhaust plenum that collects exhaust gasses output through the exhaust port or ports 56. In this regard, the turbine 121 is rotated by exhaust gas passing through it. This rotates the compressor 122, causing it to generate charge air by compressing fresh air. Charge air output by the compressor 122 flows through a charge air channel 126 to a cooler 127 whence it is pumped by a supercharger 110 to the intake ports. Charge air compressed by the supercharger 110 can be output through a cooler 129 to an intake manifold 130 or an intake plenum for provision to the intake port or ports 54. In some instances, exhaust products may be recirculated into the charge air channel through an exhaust gas recirculation (EGR) channel 131 for the purpose of reducing unwanted emissions.
The opposed-piston engine is provided with an engine control mechanization—a computer-based system including one or more electronic control units coupled to associated sensors, actuators, and other machinery throughout the engine that governs the operations of various engine systems, including the air handling system, a fuel system, a cooling system, and other systems. The engine control elements that govern the air handling system are referred to collectively as the “air handling control mechanization”.
In an air handling system for a two-stroke cycle, opposed-piston engine, the supercharger performs a number of important functions. For example, it provides a positive charge air pressure to drive uniflow scavenging through the cylinders. In addition, the supercharger delivers boost (increased air pressure) when the engine accelerates. Further, the supercharger may be employed to pump recirculated exhaust products through the EGR channel. In many instances, the supercharger is one of the key components of the air handling system in an opposed-piston engine. Deterioration of supercharger performance can have significant negative impact on the emissions, general performance, and durability of the engine.
Manifestly, it is important to monitor and diagnose the performance of the supercharger and provide clear indications when its performance falls below an acceptable limit. Accordingly, there is a need for air handling control mechanizations for opposed-piston engines that are capable of confirming that a supercharger is operating correctly, and diagnosing and reporting faults that may occur in supercharger operation.
Optimal operation of a supercharger may require an additional element that enables modulation of the pressure of charge air output by the supercharger. In this regard, it is frequently the case that the supercharger's impeller is coupled to a crankshaft by a direct drive element such that the impeller cannot rotate independently of the crankshaft. The fixed relationship between supercharger and crankshaft affords a rigid and imprecise regulation of boost (charge air compressed by the supercharger). In order to modulate boost pressure and gain greater precision in charge air handling under such conditions, a bypass valve is provided in fluid communication with the charge air channel downstream of the supercharger outlet to adjust the pressure of boost air produced by the supercharger as needed in response to engine operation. In other instances, the supercharger may be driven by a variable speed device with a transmission that enables the supercharger's speed to be controlled independently of the crankshaft.
In some instances, an apparent deterioration of supercharger performance can result from faulty performance of an element that controls or modulates the supercharging operation. For example, a sticky supercharger bypass valve or a faulty bypass valve actuator can impair the air handling system's boost response in a way that is indistinguishable from the performance of a supercharger with a defective belt. In another instance, a variable speed supercharger drive with a deteriorating transmission can cause boost pressure fluctuation, as would happen in the case of a supercharger with compromised rotors.
Manifestly, it is important to continuously monitor and diagnose the performances of elements that control or modulate supercharger operations, and to take appropriate actions if performance of such an element falls below an acceptable limit. Accordingly, there is a need for air handling control mechanizations for opposed-piston engines that are capable of confirming that air handling system elements that affect supercharger operations are operating correctly, and diagnosing and reporting faults that may occur in their operations.